Eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) are Long Chain Poly-Unsaturated Fatty Acids (LCPUFA) and belong to the omega-3 family. These polyunsaturated fats play a very important role in the function of our bodies and have been shown to be important in maintaining brain, retina and cardiovascular health (1-9). These fatty acids also play an important role in inflammation and thus they are useful for fighting diseases linked to inflammation, which include cardiovascular disease and arthritis (10-12).
The nutritional importance of EPA and DHA began emerging in the mid 1980s. The paleolithic diet contained small and roughly equal amounts on Omega-6 and Omega-3 PUFAs (ratio of 1-2:1) (13). An imbalance of this ratio can cause many age related health problems and neurodegenerative diseases (14).
In the 1980s, the major source of these LCPUFAs in the human diet was from fish or from fish oil capsules. But fish stocks are declining throughout the world due to overfishing. In addition, fish accumulate methyl mercury, PCB's and other toxins in their fat tissue, and these thus contaminate fish oils.
Fish do not synthesize EPA and DHA; they accumulate them from eating phytoplankton or eating animals that eat phytoplankton. It is the phytoplankton and other microbes that are the primary producers of EPA and DHA. Thus, an alternative source of EPA and DHA is microorganisms, and particularly phytoplankton.
A search is on to find suitable organisms to produce EPA- and DHA-containing oils (15-19).
The main difference in fish oils and algal oils is their structure. Fish oils are storage lipids and are in the form of triacylglycerides. The algal lipids are a mixture of storage lipids and membrane lipids. The EPA and DHA present in algae is mostly in the form of glycolipids and a small percentage is in the form of phospholipids. Glycolipids are mostly part of chloroplast membranes and phospholipids are part of cell membranes. Since glycolipids and phospholipids comprise a maximum of approximately 10-15% of the dry weight of algae, EPA and DHA production in this form is not considered economically viable. It has been suggested that cost effective production of EPA and DHA from algae (or any other microbes) would require the use of microbial strains that could produce large amounts of triacyglycerides (21).
Marine algae rich in EPA or DHA are produced by hatcheries in greenhouses or indoors in large tanks or transparent cylinders. But such methods are expensive and commercially not viable.
Economical ways of raising microorganisms that accumulate EPA and DHA are lacking. Microalgae have the potential to be raised photoautotrophically—by photosynthesis without a reduced carbon source, using CO2 as their carbon source. Since sunlight is free and land is inexpensive in some areas, it would be advantageous to raise microalgae outdoors photoautotrophically with sunlight in a way that results in accumulation of EPA and/or DHA. But culturing microalgae outdoors photoautotrophically is challenging because the cultures grow slowly and are prone to become contaminated when cultured outdoors. In addition, strains that may accumulate significant quantities of EPA or DHA under carefully controlled conditions may not accumulate as much under outdoor photoautotrophic conditions.
New sources of EPA and DHA for human nutritional supplements and as animal feed and aquaculture feed are needed. New improved methods of culturing microalgae to serve as a source of EPA or DHA are needed. Identification of microorganisms that are suitable sources of DHA and EPA for humans, seafood, and livestock is needed.